Removal of an undecane-rich fraction from a hydrocarbon conversion process recycle



y 1962 R. H. KOZLOWSKI REMOVAL OF AN UNDECANE-RICH FRACTION FROM A HYDRO CONVERSION PROCESS RECYCLE Filed March 50, 1959 CARBON CURVE B. RECYCLE-NO UNDECANE REMOVED CURVE C. RECYCLE-UNDECANE FRACTION REMOVED 2 O z r- E Q 0 Z u n 3 m 1L 5 lm o o u E l a: 3 s a a: U H I o O. I m 1: I

| o o o o o 10 q- N o v m m m 'A BBHLVHHdINEIJ. HOdVA INVENTOR ROBERT KOZLOWSK/ States This invention relates to a process for the catalytic conversion of hydrocarbon distillates. More particularly, it relates to an improved process for converting such distillates to products boiling essentially below the feed fractions employed.

A process has recently been developed for the conversion of petroleum middle distillates boiling generally above about 325 F. to high octane gasoline blending stocks boiling below about 325 F. The process comprises passing such a feed, along with hydrogen, to a conversion zone for contact with a catalyst comprising a hydrogenating component dispersed on an active cracking support at a pressure of at least 400 p.s.i.g. and at temperatures of from about 350 to 800 F. Although once-through operations are feasible, it has been found to be a great deal more efiicient and productive to recycle at least portions of the conversion zone effluent boiling above about 325 F. to said zone.

In operating the process with paraffin-containing petroleum distillate feeds having initial boiling points of from about 325 to 370 F. and end points above about 395 F. under conditions such that the recycle stream includes fractions boiling above about 370 F., it has been found that a comparatively narrow boiling fraction of the recycle stream is extremely refractory to subsequent conversion and tends to build up in said stream to a high level. This,

of course, is undesirable since it requires the constant recycling of a fraction that is essentially resistant to conversion and thus diminishes the amount of fresh feed which can be fed to the unit.

It was found that this build-up in the recycle stream of a refractory material is largely attributable to the presence of a single normal parafiin species, namely, undecane (B.P. 384.5 F.). Apparently this compound, entering the system in the distillate feed, is extremely resistant to the isomerization, disproportionation and selective cracking reactions that occur in the conversion zone under the relatively low temperature conditions employed therein.

Accordingly, the present invention is directed to an improved method of operation of the aforenoted recycle process which comprises reducing the undecane content of the recycle stream that is returned to the conversion Zone. While this fraction can be removed in various ways, preferably the process is operated such that at least a portion of the 375 :L-5 to 395i5 F. boiling fraction of the conversion zone effiuent is continuously removed from the reaction system, thereby essentially preventing any material undecane build-up in the recycle stream which is returned to the conversion zone. This removed fraction, due to its high normal paraifin content, may be ad- 5 boiling above 400 F. into the conversion zone'at essen 3,044,953 Patented July 17, 1962 EXAMPLE was employed as a feed stock to the conversion zone. A

distillation curve (broken line marked A) of this feed is shown on the figure of the accompanying drawing. The feed was one that is preferred for the particular conversion process in that the basic nitrogen content was below 25 p.p.m. The feed, along with 6,500 s.c.f. of hydrogen per barrel of total feed, was passed at a liquid hourly space velocity (LHSV) of 1.0 through the conversion zone wherein the feed and hydrogen were contacted with a catalyst composed of nickel sulfide (2.5 weight percent Ni) on an active silica-alumina cracking catalyst support 90% SiO 10% A1 0 The conversion zone was operated at a pressure of 1200 p.s.i.g., and an average temperature in the range of from about 650 to 800 F. which provided a volume percent conversion to products boiling below about 350 F. The unit was operated at extinction recycle,

. i.e., all of the conversion zone efiluent boiling above about 350 F. was recycled to the conversion zone. A sample of this recycle stream after 236 hours of operation (average catalyst-bed temperature of about 725 F.) was taken and subjected to a Hypercal distillation. The results f this distillation are shown on the solid distillation curve B on the figure. The large plateau in the 380 to 390 F. region, which is not present in the feed distillation curve, is readily apparent and clearly shows the build-up and consequently the refractory nature, of this portion of the recycle stream. Mass spectral analysis of both the fresh feed stock and recycle portions boiling between 380 to 390" F. gave the compositions indicated in the table below.

From the above table, it can be seen that undecane content of the 380 to 390 P. fraction builds up to volume percent, while from curve B it can be seen that this 380 to 390 P. fraction amounts to about 35 volume percent of the entire 350 F.+recycle.

The recycle stream distillation curve B plotted on the figure also shows that the large build-up of refractory compounds is largely confined to undecane. Thus, no other plateaus indicating such a large build-up are found on the recycle stream distillation curve B, and this despite the fact that some n-dodecane was present. This has also been found to be the case when a light cycle oil boiling in the range of from about 400 to 500 or 600 F. was employed as the distillate feed to the conversion zone operating with a 400 F.+extinction recycle.

It might also be noted that the undecane build-up occurs only when the compound is present in the initial feed stock. This was observed by passing a feed stock 3 tially the same conditions described in the example above and recycling the 360 F.+ product. No undecane plateau was found in the distillation curve of the recycle stream.

A third distillation curve C indicates a typical re cycle stream when an undecane-rich fraction is continuously removed from the 350 F.+ portion of the conversion zone eflluent.

The feed stocks employed in the process are those petroleum distillates containing undecane and boilingabove about 325 F., and preferably in the general range of from about 325 to 850 F. Preferably, these feeds contain over about 10 volume percent aromatic hydrocarbons and/or have basic nitrogen contents of less than 25 ppm. If the particular feed stock has a basic nitrogen content in excess of this figure, a conventional first stage hydrofining operation can be employed to denitrify the feed. In general, suitable feeds are those generally defined as naphthas, kerosene distillates, gas oils and recycle oils. These may be of straight-run origin, as obtained from petroleum, or they may be derived from various processing operations, and in particular, from thermal or catalytic cracking of stocks obtained from petroleums, gilsonite, shale, coal tar or other sources.

The catalyst employed is a multifunctional catalyst composition comprising a hydrogenating component dispersed on an active cracking support. The latter may comprise any one or more of such acidic materials as silica-alumina, silica-magnesia, silica-alumina-zirconia composites, as well as certain acid treated clays and similar materials. A preferred cracking support is comprised of synthetically prepared composites of silica and alumina containing from about 70 to 95% of the silica component.

The hydrogenating component of the catalyst may be selected from any one or more of the various group VI and group VIII metals, as well as the oxides and sulfides thereof, representative materials being the oxides and sulfides of molybdenum, tungsten, chromium and the like, together with such metals as nickel or cobalt and the various oxides and sulfides thereof. Also suitable are certain group I (B) or group II (B) metals, such as copper or cadmium and their oxides and sulfides. If desired, more than one hydrogenating component may be present. The amount of total hydrogenating component may be varied within relatively wide limits of from about 0.1 to 25%, based on the weight of the entire catalyst composition.

In the operation of the present process, the distillate feed may be introduced to the conversion zone, in admixture with hydrogen, as either a liquid, vapor or mixed liquid-vapor phase, depending upon the temperature, pressure, proportion of hydrogen and boiling range of the charge stocks utilized. The feed is introduced in admixture with at least 2000 s.c.f. of hydrogen per barrel of total feed (including both fresh, as well as recycle feed), and the amount of hydrogen may range upwardly to 15,000-20,000 s.c.f. per barrel of total feed. From about 500 to 2000 s.c.f. of hydrogen are consumed in most instances in the conversion zone per barrel of total feed converted to synthetic product, i.e., that product boiling below the initial boiling point of the fresh feed. The hydrogen stream admixed with the incoming feed is conveniently made up of recycle gas recovered from the efiluent of the conversion zone (and, if desired, from a first stage hydrofining zone if the latter is employed), together with fresh make-up hydrogen.

The pressures employed in the conversion zone are in excess of about 400 p.s.i.g. and may range upwardly to as high as 5000 p.s.i.g., with a preferred range being from about 600 to 2500 p.s.i.g. The feed may be introduced to the conversionzone at a liquid hourly space velocity (LHSV) of from about 0.2 to 5 volumes of hydrocarbon (calculated as liquid) per superficial volume of catalyst, with a preferred rate being from about 0.5 to 3 LHSV.- The process may be conducted at temperatures in the range of from about 350 to 800 F. with a preferred range being from about 450 to 700 F. This relatively low temperature operation is one of the distinguishing features of this process over conventional high emperature hydrocracking reactions.

The process can be conducted in either fixed catalyst bed, moving bed, fluid catalyst or slurry catalyst systems with the fixed bed operation being preferred. It is possihis in many cases to extend on-stream time over such long periods that it becomes uneconomic to provide catalyst regeneration facilities. However, catalyst regeneration can be effected either in situ or in separate regeneration zones,-by conventional regeneration techniques.

A preferred method of conducting the process, including the removal of the undesirable undecane-rich fraction from the conversion zone efiluent, can be briefly described as follows:

The distillate feed, a recycle stream to be described and hydrogen are passed into a fixed catalyst bed conversion zone operating within the hereinbefore defined conditions. Following conversion, the total effluent from the conversion zone (reactor) is first passed into a high pressure separator from which is removed a hydrogen-rich stream which is recycled to the conversion zone, along with fresh make-up hydrogen. The hydrogen-lean effluent is then passed to a low pressure separator wherein a normally gaseous C -(butane and lighter) stream is flashed off and removed to storage. The remaining C fraction is then passed into a separation zone, in this case a fractional distillation column, wherein this C fraction is separated into the desired fractions. For example, separation can be made into a variety of gasoline blending stocks having various boiling ranges, an intermediate fraction rich in undecane which is recovered and removed from the system, and a bottoms recycle stream that is returned to the conversion zone.

It is obvious that the separation of the conversion zone efiluent can be done in many ways. Thus, all separations could be made in one large distillation zone, or in a plurality of flash separators and/ or distillation columns. Also, the actual boiling ranges of the product gasoline blending fractions can be varied to suit the purpose of the particular refiner. The important step, insofar as the present invention is concerned, is preventing an undecanerich fraction, boiling inthe range of from about 375:5" to 395i5 F., from being returned to the conversion zone in the recycle stream which will, under most situations, boil above about 325 F. Whether the removal of this undecane fraction is done in the efiluent separation zone or zones or in a separate zone located on the recycle stream itself is immaterial.

I claim:

1. In a hydrocarbon conversion process wherein an undecane-containing petroleum distillate feed having an initial boiling point from about 325 F. to 370 F. and an end point above about 395 F. and hydrogen are contacted in a conversion zone at temperatures from 350 F. to 800 F. and pressures above 400 p.s.i.g. with a catalyst comprising a hydrogenating component disposed on an active cracking support, and wherein a recycle stream having a boiling range extending above and below the 384.5 F. boiling point of undecane is obtained from the effluent from said conversion zone and is returned as feed to said conversion zone, the improvement which comprises removing undecane from said recycle stream prior to returning said stream to said conversion zone, whereby undecane is prevented from building up in the system and reducing the capacity of said conversion zone to convert fresh feed.

2. In a hydrocarbon conversion process wherein an undecane containing petroleum distillate feed having an initial boiling point from about 325 F. to 370 F. and an end point above about 395 F. and hydrogen are contacted in a conversion zone at temperatures from 350 F. to 800 F. and pressures above 400 p.s.i.g. with a catalyst 5 6 comprising a hydrogengating component disposed on an building up in the system and reducing the capacity of active cracking support, and wherein a portion of the said conversion zone to convert fresh feed. I efiiuent from said conversion zone having a boiling range extending above and below 375 :5 F. to 395i5 F. is References Cited in the file of this patent returned as feed to said conversion zone, the improvement 5 UNITED STATES PATENTS which comprises removing from said portion prior to the return thereof to said conversion zone the fraction boiling 2,428,692 Voorhles 1947 from 375 i5 F. to 395: :5 F. and containing undecane, 2,858,267 Knnedy et 1958 and returning only the remainder of said portion to said 2,902,436 M1115 P 1959 conversion zone, whereby undecane is prevented from 10 

1. IN A HYDROCARBON CONVERSION PROCESS WHEREIN AN UNDECANE-CONTAINING PETROLEUM DISTILLATE FEED HAVING AN INITIAL BOILING POINT FROM ABOUT 325*F. TO 370*F. AND AN END POINT ABOVE ABOUT 395*F. AND HYDROGEN ARE CONTACTED IN A CONVERSION ZONE AT A TEMPERATURES FROM 350*F. TO 800*F. AND PRESSURES ABOVE 400 P.S.I.G. WITH A CATALYST COMPRISING A HYDROGENATING COMPONENT DISPOSED ON AN ACTIVE CRACKING SUPPORT, AND WHEREIN A RECYCLE STREAM HAVING A BOILING RANGE EXTENDING ABOVE AND BELOW THE 384.5*F. BOILING POINT OF UNDECANE IS OBTAINED FROM THE EFFUENT FROM SAID CONVERSION ZONE AND IS RETURNED AS FEED TO SAID CONVERSION ZONE, THE IMPROVEMENT WHICH COMPRISES REMOVING UNDECANE FROM SAID RECYCLE STREAM PRIOR TO 